The following relates to hypodermic syringes, and more particularly relates to a dental syringe utilizing disposable carpule assemblies of the type in which the hypodermic needle can be destroyed after use so as to prevent its reuse, such as, for example, by drug abusers.
I previously devised a dental syringe utilizing a disposable carpule in which the hypodermic needle can be completely retracted into the carpule after use and thereby allow an operator to dispose of the carpule and needle without coming into direct contact with the needle. Reference is made to my U.S. Pat. No. 6,248,094. As noted in my patent, other syringes have been devised with a single-use, disposable syringe having a fluid containment system which complements the respective retractable needle assembly. Even so, there continues to be a need, particularly in the dental field, for a retractable needle assembly in which the injectable end of the needle can be completely destroyed prior to retraction into the carpule assembly after its use and in this way prevent cross-contamination or other accidental injury to the operator when delivering an injectable solution to a patient. For example, in accordance with my '094 patent, the needle assembly can be fully retracted into the carpule following use and the one end of the needle opposite to the injectable end can be at least partially destroyed but in doing so moves the needle assembly out of alignment with the exit end of the syringe so that it cannot be extended again through the opening without considerable trial and error; and even then cannot be fully extended so as to be accessible for complete destruction or severance of the injection end from the rest of the needle assembly. Still further, after destruction, it is desirable to once again be able to retract the remainder of the needle assembly into the carpule and remove from the syringe for disposal. In this relation, there is also a need for a guide assembly at the end of the syringe in which a portion of the guide can be removed after the needle injection and retraction into the carpule which will enable maximum exposure of the injection end of the needle when it is once again extended from the carpule assembly for destruction.